a) Field of the Invention
The present invention relates generally to an engine valve assembly having a valve lifter interposed between an engine valve body such as an intake or exhaust valve and a cam pressing the engine valve body under a given pressure.
b) Description of the Related Art
A U.S. Pat. No. 5,749,341 issued on May 12, 1998 exemplifies a previously proposed valve lifter for an internal combustion engine.
The valve lifter disclosed in the above-described United States Patent includes a recess portion formed on an upper surface of a summit wall of a bell-shaped cylindrical main body; and a shim for adjusting a valve clearance housed in the recess portion. A circular groove which communicates each through hole at the recess portion with the shim is formed on an upper surface of a bottom wall of the recess portion. A lubricating oil dropped on an upper surface of the shim is dropped on a spring retainer via the shim and through hole of the recess portion. The lubricating oil jumped from the spring retainer due to an operation of a valve spring is supplied to a contact portion between a valve stem and the valve lifter.
However, in the engine valve assembly disclosed in the above-identified United States patent, the shim for adjusting valve clearance is attached onto the valve lifter separately from the main body of the valve lifter. Hence, due to a friction (frictional force) developed on a slide portion between the cam and adjusting shim along with revolution of the cam, this adjusting shim only is revolved and the valve lifter main body itself is not revolved.
That is to say, the friction between the adjusting shim and valve lifter when the adjusting shim is revolved causes a torque to be transmitted to the main body of the valve lifter itself. However, since the frictional force between an outer periphery of valve lifter and a guide hole of a cylinder head to guide a slid motion of valve lifter main body is larger than the frictional force between the shim and valve lifter main body, the valve lifter main body is rarely revolved but the lubricating oil is dropped onto a portion at which a quantity of lubricating oil becomes substantially constant.
In a case where the valve lifter is inclined with respect to the cylinder head and the valve lifter is not revolved with the outlet of the through hole placed at a lowest end portion, almost all of lubricating oil from the outlet of the through hole is transmitted onto the inner surface of the valve lifter. Even if the lubricating oil is dropped onto the spring retainer. A very small quantity of lubricating oil is dropped onto the spring retainer. Consequently, a sufficient lubrication cannot be carried out in a contacting portion between the valve stem and valve lifter and spring retainer.
It is, therefore, an object of the present invention to provide an engine valve assembly for an internal combustion engine in which a sufficient lubrication can be carried out for a contact portion between the valve stem and valve lifter and the spring retainer even if the valve lifter is disposed on the cylinder head obliquely with respect to a direction of gravity.
The above-described object can be achieved by providing an engine valve for an internal combustion engine, comprising: a valve lifter comprising a cylindrical main body portion and a head wall portion by which an opening of the cylindrical main body portion is enclosed and with which a cam is brought in contact; a valve stem contacted on an axial center of the valve lifter and disposed obliquely with respect to a direction of gravity; a lubricating oil supply bore whose exit is opened to an inner space of the head wall portion and is revolved due to a revolution of the valve lifter caused by a friction developed on the basis of a revolution of the cam; and a spring retainer to support an end of a valve spring, the spring retainer being attached onto the valve stem.
The above-described object can also be achieved by providing an engine valve for an internal combustion engine, comprising: a valve lifter comprising a cylindrical main body portion and a head wall portion by which an opening of the cylindrical main body portion is enclosed and with which a cam is brought in contact; a valve stem contacted on an axial center of the valve lifter and disposed obliquely with respect to a direction of gravity; a lubricating oil supply bore whose exit is opened to an inner space of the head wall portion and is formed in plural for each predetermined interval of distance in a circumferential direction of the head wall portion; and a spring retainer to support an end of a valve spring, the spring retainer being attached onto the valve stem.
The above-described object can also be achieved by providing an engine valve for an internal combustion engine, comprising: a valve lifter comprising a cylindrical main body portion and a head wall portion integrally formed with the cylindrical main body and by which an opening of the cylindrical main body portion is enclosed and with which a cam is brought in contact; a valve stem contacted on an axial center of the valve lifter and disposed obliquely with respect to a direction of gravity; a lubricating oil supply bore formed to penetrate through the head wall portion and whose exit is opened to an inner space of the head wall portion and is revolved due to a revolution of the valve lifter caused by a friction developed on the basis of a revolution of the cam; and a spring retainer to support an end of a valve spring, the spring retainer being attached onto the valve stem.
The above-described object can also be achieved by Providing an engine valve for an internal combustion engine, comprising: a valve lifter comprising a cylindrical main body portion and a head wall portion by which an opening of the cylindrical main body portion is enclosed and with which a cam is brought in contact; a valve stem contacted on an axial center of the valve lifter and disposed obliquely with respect to a direction of gravity; a lubricating oil supply bore whose exit is opened to an inner space of the head wall portion and is revolved due to a revolution of the valve lifter caused by a friction developed on the basis of a revolution of the cam and whose inlet is formed on an upper surface of the head wall portion on which the can is contacted, an opening edge of the inlet of which is formed in an arc shape; and a spring retainer to support an end of a valve spring, the spring retainer being attached onto the valve stem.